Membranes for anatomical prostheses such as breast prostheses are commonly formed by applying a solution or suspension of a copolymer and a solvent, evaporating the solvent and then curing the copolymer in place. One well-known copolymer is methyl-trifluoropropyl siloxane-dimethylsiloxane, available as a fluorosilicone elastomer dispersion.
For application this dispersion is dissolved in an evaporable solvent. A widely used solvent at the present time being 1.1.1 trichloroethane (for convenience hereafter referred to as "trichloro"), which functions well for this intended use. However, this solvent has been identified as an ozone depleter and is being phased out from industrial use. Other suitable solvents include chloro-fluorocarbon solvents with also have ozone depleting properties as well as high cost.
If it were not for the serious extraneous problems of trichloro, there would be little purpose for this invention. Its equivalent has been most elusive because of the necessity to produce a membrane from a deposited and cured copolymer that reliably provides a barrier against the migration through it of typical fillers such as dimethyl silicone-based gels, and also of materials such as are described in Tiffany U.S. Pat. No. 4,731,081 among others. All of this while being environmentally benign and non-flammable.
As one seeks substitutes for trichloro, it soon becomes evident that the obvious ones themselves often have serious drawbacks, for example, extreme flammability, hydroscopicity, and poor solubility of the dispersion or being ozone depleting. P. suitable replacement should be non-flammable, have a boiling point range between about 90 degrees to 150 degrees C., and be an excellent solvent with reasonable cost. These parameters are determined by the need to provide a good clear "true" solution, and also a safe one for use in the manufacturing process, and for environmental compatibility.
Further, for manufacturing a low-permeability membrane, it has been commonly assumed that a high mole percentage of the fluorosilicone moiety, perhaps as high as 90% mole ratio, should be used. Applicant has found that a surprisingly lower mole percent from 15-50% of this moiety can be used to form membranes which are as effective as those made from the higher mole percentage fluorosilicone when using the solvent of this invention when used to produce a membrane of reduced polarity and permeability to dimethyl silicone fluids.